The present invention relates to a process for producing a single crystalline semiconductor island on an insulator.
It is well known to use a so-called silicon-on-insulator (SOI) structure to form an integrated circuit device with a three-dimensional structure and thus improve the integration of a semiconductor integrated circuit device.
In an SOI structure, it is essential to form single crystalline semiconductor islands on an insulator so as to form a semiconductor device. This is usually achieved by forming a polycrystalline or amorphus semiconductor layer on a silicon oxide insulator layer or substrate, dividing the semiconductor layer into islands, and then melting and recrystallizing the semiconductor islands into single crystalline semiconductor islands using, e.g., an argon ion laser beam.
It is difficult, however, to achieve uniform cooling and recrystallization of semiconductor islands. This is because only the silicon islands absorb the energy of the argon ion laser beam. Therefore, thermal diffusion to the unheated silicon oxide insulator reduces the temperature along the island edges.
Considerable research has been performed aimed at producing single crystalline semiconductor islands on an insulator. One approach has been to provide the silicon substrate under the central portion of the islands with a conductive path having a thermal resistance lower than that of the surrounding areas so as to accelerate cooling of the central portion of the islands. This process, however, cannot be applied to produce a three-dimensional structure.
J. P. Colinge et al. report a process in "Use of Selective Annealing for Growing Very Large Grain Silicon on Insulator Films", Applied Physics Letter 41 (4), Aug. 15, 1982, page 346, in which silicon wafers are thermally oxidized and capped with a polycrystalline silicon layer which is, in turn, capped with a patterned silicon nitride layer. When the wafers are scanned with an argon ion laser, silicon nitride works as an antireflective layer. The polycrystalline silicon under the silicon nitride therefore exhibits a higher temperature than that of the surrounding area. Colinge's concept can be applied to selective annealing of a polycrystalline silicon layer for forming a three-dimensional structure integrated circuit device, however, it has the disadvantage of involving the additional troublesome step of patterning the silicon nitride layer by means of photolithography.
W. G. Hawkins et al. report a process in "Growth of Single-Crystal Silicon Islands on Bulk-Fused Silica by CO.sub.2 Laser Annealing," Applied Physics Letter 40(4), Feb. 15, 1982, page 319, in which CO.sub.2 laser radiation is used. Generally, silicon oxide will absorb CO.sub.2 laser radiation, while silicon islands will substantially not. Hawkins et al. showed that the silicon oxide surrounding the islands would absorb about 87 percent of the incident energy, while the silicon dioxide under the islands would absorb only 70 percent. Consequently, the island edges are much hotter than the central portions. In the process of Hawkins et al., however, it is necessary that the silicon oxide be thick enough to absorb the CO.sub.2 laser energy so as to melt the silicon islands. This process is therefore not suitable for producing a three-dimensional structure.
Incidentally, Hawkins et al. remark that the reproducible growth of oriented single crystalline silicon islands through use of an argon ion laser has not yet been demonstrated, although they recognize much progress has been made toward understanding mechanisms which control crystal growth under argon ion laser irradiation.